Display device with sliding back plates

A display device comprising an opaque face plate having at least one array of openings therein arranged to represent predetermined indicia when light is transmitted through selected openings of said array, an opaque back plate slidably mounted behind said face plate and having an array of light passages therein, some of which are elongated slots which are of substantially greater length than the corresponding dimension of openings in the face plate, means guiding said back plate for reversible stepped sliding movement in a predetermined lineal direction that corresponds with the direction in which said elongated slots extend, portions of said light passages in said back plate permitting light to be transmitted through selected openings of said face plate while said opaque back plate blocks the transmission of light through other openings and said slots being arranged so some will be between openings in said face plate while other of said slots are coincident with corresponding openings, thereby forming selected indicia, some of said face plate openings being arranged in a line extending in one direction and said elongated slots being arranged in rows each comprising slots of varying length, said rows being parallel to each other and inclined at an acute angle relative to said line, and drive means coupled to said back plate for shifting said back plate linearly, said elongated slots being so disposed relative to said face plate openings that when the back plate is shifted in its guided path there is a change in the selection of openings in the face plate through which light is permitted to pass, thereby changing said indicia.